1. Field of the Invention
This invention relates to an image processing apparatus, for use in a laser printer, a digital copying machine, or a digital facsimile. The invention particularly relates to an image processing apparatus, which achieves smooth enlargement and multilevel output of an image.
2. Related Art
There is a smoothing technique which is done by enlarging binary image data an integral number of times. The binary image data are enlarged and supplemented to smooth a jaggy image, for example a slant line, referring to image data adjacent to aimed data or datum. Therein the output is binary data. This technique is currently used in facsimile machines and the like.
Moreover, there is a high quality image technique which is done by multileveling the jaggy image of the binary image data in a printer which can output a multilevel image. An example of such a printer is an RET (Resolution Enhanced Technology) by Hewlett Packard company. Printer manufacturing companies use that printer or similar ones.
On the other hand, a digital copying machine has recently been introduced that is multifunctional. The product is schematically shown in FIG. 7. The system comprises a digital copying function as a central function, a printer function for printing a document by a word processor and the like, a scanner function for scanning an image and storing it as a data-base file, and the like, a facsimile function for transmitting and receiving a facsimile image, and a network function for printing image data from a network and sending an image by a scanner to a network.
Table I indicates enlargement ratios when three kinds of facsimile (FAX) image are printed in three kinds of printer which have resolutions of 300 dpi, 400 dpi, and 600 dpi. For example, a facsimile image of 8 (dot/mm).times.7.7 (dot/mm) is enlarged at twice vertically and horizontally to print its facsimile image in a 400 dpi printer. Moreover, the printer of a recent digital copying machine can output multilevel tones. Therefore a system for printing a facsimile image which has the smoothing enlargement function and multilevel output function is required.
TABLE 1 ______________________________________ enlargement ratio 300 dpi 400 dpi 600 dpi (12 (16 (24 (dot/mm) .times. (dot/mm) .times. (dot/mm) .times. Fax Image 12 (dot/mm)) 16 (dot/mm)) 24 (dot/mm)) ______________________________________ 8 (dot/mm) .times. 1.5 .times. 3 2 .times. 4 3 .times. 6 3.85 (dot/mm) 8 (dot/mm) .times. 1.5 .times. 1.5 2 .times. 2 3 .times. 3 7.7 (dot/mm) 16 (dot/mm) .times. -- 1 .times. 1 1.5 .times. 1.5 15.4 (dot/mm) ______________________________________